Method of making fiber optical components



July 18, 1961 F. H. NORTON METHOD OF MAKING FIBER OPTICAL COMPONENTS 2Sheets-Sheet 1 Filed July s, 1957 JNVENTGR FEEDER/CK H. NORTON July 18,1961 F. H. NoRToN 2,992,515

METHOD OF MAKING FIBER OPTICAL COMPONENTS Filed July 3, 1957 2Sheets-Sheet 2 v '00 ||||||I||||||mmm||||||||||||||||||||i gig/Z NVEA/TOE FEEDER/CK l1'. NORTON United States Patent O 2,992,516 METHOD FMAKING FIBER OPTICAL COMPONENTS Frederick Harwood Norton, Boston, Mass.,assignor to American Optical Company, Southbridge, Mass., a voluntaryassociation of Massachusetts Filed July 3, 1957, Ser. No. 669,883Claims. (Cl. 49-79) This invention relates to a method of manufacture oflight-conducting fiber optical devices and components of novelconstruction. More particularly, the invention relates to a method ofmanufacture of light-conducting fiber optical devices and components byan assembling, fusing and drawing technique so that each fiber opticalcomponent or device produced thereby will be produced in a moreefficient, rapid and accurate manner and will comprise a very largenumber of very small similar lightconducting fibrous elements orfilaments positioned in part or entirely in side-by-side groupedrelation to each other in such a manner that each individual element orfilament thereof will function independently and efiiciently inconducting light from one end thereof to the other, and collectively allof the filaments will function to provide an image transfer device orcomponent having good resolution and contrast.

It has been known for a long time that many thin long transparentfilaments of glass can be hunched together and used to transmit lightand even transmit an optical image from one location to another, butthis has n only been accomplished with a limited degree of success.Prior devices of such character have not been as satisfactory as mightbe desired due largely to the fact that light from one filament wouldescape or scatter to an adjacent filament or even to several adjacentfilaments, both at points of contact between the filaments and at arcassurrounding these points, and would not only deteriorate the quality ofthe light within individual filaments but would also have the overalleffect of confusing the definition and contrast of the image beingtransmitted. Thus the reproduced image would appear washed out and theparts of the image which should appear sharp and clear would actuallyappear roughed and blurred. Attempts have been made to prevent thisoptical interaction between filaments, as for example, by cementing thefilaments together by the use of a black paint or by keeping thefilaments air spaced from one another. But such attempts have notproduced successful devices. Too much light was absorbed in the one caseby the black paint and too much space was lost between filaments at theend of the device in the other case thereby naturally reducing the imageresolution which could be obtained. Furthermore, when the number oflight-conducting fibers or filaments for forming an image transferdevice is increased to give high degrees of image resolution, theproblem of assembly becomes increasingly more difficult, because it isnecessary to have each fiber of the bundle being formed positioned inthe bundle in an orderly array since the reproduced image at the exitend thereof depends directly upon the arrangement of the individualfibers at the entrance end of the bundle. For example, if a transferdevice of four inches in cross-sectional area is to be produced and ifas many as 250,000 filaments per square inch are to be employed, theproblem of assembly alone has been heretofore practicallyinsurmountable. The method of the present invention has greatly reducedthe difficulties of forming optical image -transfer devices of theabove-mentioned character.

In co-pending OBrien application Serial No. 469,877, now issued asPatent No. 2,825,260, however, there is disclosed an optical imagetransfer device in which such optical interaction between individualfilaments of the 2,992,516 Patented July 13, 1961 very large number ofvery small filaments of the device is prevented and thus good imagecontrast and resolution are obtained. This improved device, it should benoted, comprises not only `a very large number of very small filamentseach having a core of light conducting high index material but also haseach individual core completely coated throughout its length with a verythin layer of transparent material of a lower refractive index; and eachcoating is applied in such a way that good optical contact with thesmooth outer surface of its supporting core is accomplished before themany filaments for making up Ia bundle are actually bunched together.Thus in the finished assembled device or component each core isoptically insulated from the next and the bunched ends of adjacentfilaments provide a cross sectional end area of very high lightaccepting efficiency.

The present invention provides a method by which optical image transferdevices and components of the above improved type may be made.

It is accordingly an object of the present invention to provide a novelassembling, fusing and drawing method for producing optical devices andcomponents comprising in each case a plurality or even a very largenumber of small or very small elongated light-conducting elements i'positioned in fixed sideby-side parallel relation to each other, atleast at an end portion thereof, as well as fused optical image transfercomponents.

It is also an object of the present invention to provide a method bywhich such optical image transfer devices and components, both tapered'and straight sided, may be made having suitable means for ensuringtransmission of a very high degree of the light which enters theindividual elements or filaments at one end thereof through the entirelengths of the elements without appreciable loss of light therefrom.

It is an additional object of the invention to provide a method forproducing optical devices and components having the abovecharacteristics and which are either of a rigid or semi-flexible, oreven exible nature.

Other objects and advantages of the invention will become apparent fromthe detailed description which follows when taken in conjunction withthe accompanying drawings in which:

FIG. 1 is an elevational view of an assembly of parts for use incarrying out the method of the present invention;

l FIG. 2 is a cross-sectional view taken substantially uponsection-lines 2--2 of FIG. l and showing parts considerably enlarged;

FIG. 3 is a vertical sectional view of apparatus for use in carrying outsteps of said method and showing parts enlarged to a different scale;

FIGS. 4 and 5 are cross-sectional views of other forms which the partsof the assembly of FIG. 1 may have for carrying out the invention;

FIG. 6 is a cross-sectional View of an assembly of parts for use informing a component of the type shown in FIG. 4;

FIG. 7 is a sectional view of apparatus which may be used in performingassembly and fusing steps of said method;

FIG. 8 is a sectional view of different apparatus for use in performingfusing and drawing steps of said method;

FIG. 9 is a sectional view taken substantially upon section line 9-9 ofFIG. 8;

FIG. 10 is a sectional View of apparatus for use in performingadditional steps of said method;

FIG. 1l is a side elevational view of an optical image transfer devicemade in accordance with the present invention; and

FIG. 12 is a sectional view of a different form of optical imagetransfer device embodying the present invention.

In FIG. l is shown a plurality of thin elongated shafts or rods 12 ofglass positioned together in side-by-side parallel contacting relationto each other so as to form a bunch or bundle 14. This bundle may be, asclearly indicated in the enlarged cross-sectional view of FIG. 2, formedof rods or shafts of like size and cross-sectional shape, and generallybut not necessarily the bundle will be of a thickness which isapproximately equal to the Width thereof. These rods are for conveniencein carrying out of the method preferably all of approximately the samelength.

As will be clear from inspection of FIGS. 4 and 5, as Well as FIG. 2,while the rods of an individual fused together bundle of rods are oflike size and cross-sectional shape, nevertheless, both the size and thecrosssectional shape of the rods for the forming of different bundlesmay differ appreciably. That is to say, the crosssectional shape ofindividual rods of a bundle may be generally round as indicated at 16 inFIG. 2; or square as indicated at 18 in FIG. 4; or hexagonal asindicated at 20 in FIG. 5, or of some other geometrical shape, ifdesired; it being Well to keep in mind, however, that the preferredarrangement is that which will have as much of the end area of such abundle of rods as possible available and suitably prepared for receivingincident light for transmission through the bundle. However, in certaininstances, it may be that the square shaped rods 18 of FIG. 4, forexample, will be preferable to the circular rods 16 of FIG. 2 since, inthe case of square rods, most or all of the voids between or among therods will be substantially eliminated and more area will be availablefor light transmission. Additionally if a hermetical seal is required,such voids can be, by such a geometric pattern, completely avoided.However, at other times it may be more desirable to provide a certaindegree of porosity in the finished image transfer device or componentand in such a case circular rods, as shown in FIG. 2, or the like mightbe preferred. It may be that the use of other shapes of rods will be, atother times, preferred.

Each rod or shaft 12 to be employed in the forming of the bundle 14 ispreferably formed of a glass of good optical or ophthalmic propertiesand of a fairly high refractive index so that a high degree of internalreflection will be obtained. While plain uncoated circular rods willprovide fair results for certain purposes in finished image transferdevices produced therefrom, it is preferred to first apply about eachrod, whether of circular shape or otherwise, an outer thin surface layeror coating of glass of a relatively lower refractive index; and anassembly having such an arrangement of circular cores 22 of high indexglass and outer coatings 24 of low index glass is indicated by way ofexample in FIG. 2, and another assembly having high index glass cores 26of square cross-section and low index glass coatings 28 is indicated inFIG. 6. This outer low index layer 24 or 28 may be, for instances,integrally secured in place upon the cores 22 or 26 by momentarilydipping each rod into a molten batch of glass of lower refractive index.Any other suitable method of applying a thin uniform contnuous low indexglass layer to the core 22 or 26 may be employed. It is important,however, that such an outer layer or coating of low refractive index benot only relatively thin but also entirely continuous; the thinnessbeing so that a minimum of the total end area of the resulting fusedbundle of rods will be utilized by the combined areas of all outercoatings or layers, and the continuity requirement being so that highinternal reflection of light at all places along the length of each corewill take place at the interface between the low index coating and thehigh index core later when the finished device, resulting therefrom, isput into service.

If a plurality of glass rods are clamped or secured together in a bunchand this bunch then hung in a vertical position in a furnace or the likeand slowly heated to their softening temperature and maintained at thistemperature while the rods of the bundle elongate under their ownweight, or are drawn out, each rod will elongate intermediate theclamped ends thereof. Furthermore, each rod will retain its ownindividual cross-sectional shape during such elongation and eachstretched out portion will be spaced from the stretched out por` tionsof adjacent rods of the bundle. In other words, no adhesion or stickingtogether of adjacent rods as would be desired for carrying out of theinvention under these conditions will occur.

Instead of such a procedure, it has been found, for example, that aplurality of rods may be placed together in a suitably shaped recess ina ceramic or carbonaceous support, or even in a metal or metal cladsupport, such as is generally indicated by the support 25 in FIG. 3having an elongated recess 29 of proper size, and slowly heated in airor in a vacuum to bring the rods to a fusing temperature. (Of course,the temperature to which such a bundle of rods is raised will dependdirectly upon the particular melting characteristics of the glasscompositions on the outer surface of the rods being used), but it shouldbe such as to cause a fusing or welding of the contacting portions ofadjacent rods into an integral member or cluster without producing orallowing any undesired change in shape to occur either in the coatingson the rods or in the cores thereof.

While the support 25 is shown with the rods 12 in a horizontal positiontherein, such a support could be provided with a sui-table cover member(not shown) arranged to press lightly on the rods in the recess 29 ofthe support while the rods are being heated and fused; and in such acase these rods would not need to be in any particular position. Also,as will later appear, other means may be used to clamp a plurality ofrods together during fusing, without being dependent upon the specificposition of the rods.

When the fused assembly or cluster of rods has cooled sufficiently toallow it to be moved without injury, it may be transferred to a tubetype furnace, or equivalent heating unit, and heated, preferably at oneend portion only, to its softening temperature. When the temperature ishigh enough, that is, when the glass at the end of the fused bundle hasbecome uniformly quite soft, the free end of this softened glass may bedrawn out at a uniform and continuous rate into a small multi-fiberedrod or strand of greatly reduced cross-sectional size. Under suchconditions, the individual coated rods of the initially fused bundleWill remain fused together and the geometric pattern of the fused partsthereof will remain unaltered even though the cross-sectional size ofthe resulting multibered strand as Well as the cross-sectional sizes ofthe several individual fibers thereof will be simultaneously greatlyreduced.

For example, it has been found in practice possible to coat the outersurface of individual 3/16" high index rods of glass (having arefractive index in the neighborhood of approximately 1.61 to 1.75) withan outer thin layer of low index glass (having a refractive index in theneighborhood of approximately 1.52 to 1.54), to assemble and fuse aplurality of these individually coated rods together to form a unitaryassembly or cluster. (Such an assembly might vary in actual commercialuse of the invention in cross-sectional size from approximately 3/1 ofan inch to 4 or 6 inches in diameter.) Thereafter the free end of thisfused assembly was heated to a softening temperature and drawn out as acontinuous multibered strand having substantially the samecross-sectional shape but of a greatly reduced size; reduced fromapproximately of an inch down to approximately 0.10 of an inch. If ithad been desired, this strand could have been reduced even more duringthis initial drawing operation. Thus, even though the cross-sectionalsize of the fused bundle was reduced as much as to 1 in a single drawingstep, nevertheless, its geometric cross-sectional configuration wassubstantially unchanged.

Such a multitibered strand is relatively stiff. Accordingly, from thestandpoint of both convenience and efiiciency during production, thestrand being continuously drawn out may be periodically severed intoequal lengths and grouped or stacked together to form a second bundle. Abundle of strands of this size might find utility in certain placeswherein only a moderate degree of image resolution is required since theseveral light-conducting fibers thereof are of fairly smallcross-sectional size. Furthermore since strands of this size may beflexed small amounts, it may be that at times one may Wish to takeadvantage of this flexibility; such as in aligning the hunched ends ofsuch a bundle of strands with elements of an associated opticalapparatus. In other instances a group of these multifibered strands maybe slowly heated to a temperature wherein the strands will soften enoughto allow all of the strands to be simultaneously shaped or curvedintermediate their ends.

In cases wherein a higher degree of resolution than that mentioned aboveis desired or required, in optical images being transferred by theimproved device or component, the additional procedure may be followedto produce a finished structure which will have a very large number ofoptically insulated filaments of very small cross-sectional size, eachfilament thereof providing a separate and independent path for a portionof the light of the image being transferred thereby.

A sizable number of such multifibered strands may be grouped together toform a bundle and clamped together, or positioned in a suitably shapedrecess in a ceramic support, or the like, and slowly heated to fusethese strands together. Thereafter this bundle will be heated slowly atone end thereof and a thread composed of many fine optically isolatedfilaments withdrawn therefrom; the number of filaments of coursecorresponding to the number of cores used initially. The cross-sectionalsize of such a thread can be controlled during drawing by control of theamount of heat being applied to the end portion of Ithe fused bundle ofstrands and by the rate at which the thread is withdrawn.

Of real interest, however, is the fact that the resulting thread,nevertheless, will still retain very closely the geometric patternoriginally provided the bundle and each filament will have a core ofhigh index material optically separated or optically isolated fromadjacent filaments by a surrounding layer or coating of low indextransparent material.

Many lengths of these multifilament threads are then grouped or hunchedtogether to build up an assembly having the cross-sectional end areadesired. The threads of the assembly may be secured together at one orboth ends, or even throughout a preselected portion thereof, or eventhroughout the entire length of the assembly by suitable binding means,or by cement or even by fusing the threads thereof together.

By such a procedure, an optical device or component having anappreciable area may be built up and this device or component will havea much higher degree of image resolution. lIt is also possible toutilize such an assembly of multifilament threads which have beensecured together throughout an extended length thereof by cutting byknown means this secured together length of threads into a number ofshorter sections for finishing into .optical components. Generally, butnot always, the end surface or surfaces of such an optical componentwould be optically finished in known manner, as by grinding, orpolishing, or both, so as to readily transmit light therethrough. lf anend of the component, however, is to be immersed, for example, in aliquid of like refractive index grinding and polishing of the endsurface would not be required.

It may be desirable to further reduce the cross-sectional size of themultifilament threads just described, as for example, wherein evengreater image resolution provided by the finished optical device isdesired. 'I'his can be obtained by repeating the assemblying, fusing,drawing and finishing steps mentioned above. vIt has been found, forexample, that starting with a fused bundle of V16 inch coated rods thebundle can be reduced to a thread of as little as 0.001 of an inch oreven smaller. Microscopic examination of cross sections of suchmultifilament threads produced by this method nevertheless reveals thateach individual filament thereof retains its original shape. Such athread is quite flexible. Thus, if a large number of these threads, eachhaving such a multifilament construction, are bundled together at theiropf posite ends, a very flexible image transfer device can be produced.

In assembling and fusing together a number of individual coated rods, itmay be desirable to employ a recessed support of modified design andsuch a support is shown at 37 in FIG. 7. This support is of a typehaving a V-shaped receiving groove or recess 38 therein with the slopingsidewalls thereof disposed at to each other as indicated by the numerals39 and 40. A cover member having a similarly shaped recess is indicatedat 42; and in a preferred construction both the recess in the support 37and the recess in the cover member 42 would have end walls so as tocompletely enclose and confine the entire assembly during fusing.Additionally the cover and support would be made of suitable heatresistant material and would be made to tit closely and even pressslightly upon the assembled coated rods. In this manner a good contactbetween adjacent surfaces of the rods will be assured during the fusingoperation. When such a support and cover are used together the fusingoperation can be performed with the assembly disposed in a vertical,horizontal or any other position desired. It may even be desirable toperform the fusing step in an oven which has been evacuated.

The fusing together of a plurality or bundle of transparent coated rodslike those shown at 12 in FIG. l, may also be carried out in thefollowing manner. A plurality or bundle of coated rods which may betemporarily held together in properly assembled relation by suitablemeans (not shown) is slowly fed into and through a bore 44a in a firstheating element 44 (see FIG. 8) and into a gripped position between apair of slowly rotating rollers 45 and 46. These `rollers are mounted ona pair of drive shafts 48 and 50 journaled respectively in blocks 52 and54 and are turned in opposite directions by drive means of knownconstruction 55.

As clearly indicated by double headed arrows 56 and 58 in FIG. 9, theseblocks 52 and 54 are shiftable toward and away from each other bysuitable means (not shown) so that all of the rods of the bundle 43 willbe held in firm contact with one another. The rollers 45 and 46 havetheir peripheral surfaces 45a and 46a recessed and these recessedsurfaces are carefully controlled in accordance with the size and shapeof the bundle of rods to be gripped thereby so that all of the rods ofthe bundle will be pressed uniformly inwardly toward each other. Forexample, in instances wherein the coated rods of the bundle are square(see FIG. 9), the surface shapes of the two rollers 45 and 46 will besuch as to provide a space therebetween which is substantially square.Or if a round bundle of rods is to be formed, for example, then thetransverse shape of the peripheral surface of each roller of the pairmay be made substantially semi-circular, and thus the two rollerstogether will define a nearly circular space for confining the rods ofthe bundle therebetween. Other shapes of bundles of rods can be formedby the use of other transverse surface shapes for such a pair ofrollers.

The blocks 52 and 54 besides being shiftable are also constructed andarranged to function as heating elements (preferably electricallyheated) which may be readily 7 controlled to maintain whatevertemperature is desired. Thus in the region adjacent the rollers 45 and46 a fusing zone 59 will be formed. 4Of course, the bundle of coatedrods 43 approaching this fusing zone will be most likely preheated bythe heating element 44.

Immediately following and adjacent lthis fusing zone 59, there is shownanother heating element or elements 60, which may be separatelycontrolled and preferably operated at a somewhat higher temperature thanrequired for the fusing operation. The purpose of heating elements 60 isto provide a working zone 62 wherein the fused bundle of rods may bedrawn out into a multi-tibered strand of considerably reducedcross-sectional size as indicated at 64. One or more pairs of poweroperated rolls 66 may be provided for this purpose, `it being understoodof course that they will be located far enough away from the drawing orworking zone 62 so as not to deform the strand in an undesired mannerwhile soft, and also understood that their rates of travel will beregulated in accordance with `the temperature of the drawing zone, sothat a desired size of multibered strands will be formed.

As suitable lengths of this multibered strand are produced they may besheared and stacked together. An optical component or device providinglow image resolution can be formed from such strands by cementing orfusing same -together in side-by-side relation. Or if a higher degree ofimage resolution is desired it may be desirable to group a number ofsuch strands together, and in substantially the same manner as mentionedabove allow this group of strands to slowly travel between a secondsimilar pair of pressure rolls in a fusing zone, and then after fusingbe again heated to a softening temperature and drawn out even further.

Thus the fused together strands having a number of optically separatedlight paths therethrough will be greatly reduced in size yand eachindividual light path thereof will be likewise reduced. Nevertheless, inthis manner the original coated cores 12 can be reduced in one, two oreven more cycles of operation each including the steps of assembly,fusing, softening, drawing and reassembly until a plurality ofmicroscopic filaments or optically separated light paths of nearly anycross-sectional size desired can be produced.

In FIG. l is shown a modified form of apparatus by which multifiberedstrands, or the like, having a controlled amount of taper therein may beproduced. In this apparatus the fused together bundle of rods or strandsare indicated at 68 being moved Slowly through the apparatus in thedirection Iindicated by the arrow 70 by driven rollers 72 and by othersnot shown. The leading end of the bundle 68 will be, by the time itreaches and passes beyond the rollers 72, heated by the preliminaryheater 74 to such a temperature that it will start to soften.

However, as this bundle of rods or multifibered strands moves forward apair of gripping fingers diagrammatically indicated in full lines at 76will simultaneously travel toward the forward end of this strand andgrip the end of the strand as indicated by the dotted lines 76A.Thereafter the fingers 76 will be caused to move (by means not shown) inthe opposite direction at a controlled rate of speed which will be suchas to draw out the end of the bundle into the taper desired. Thisdrawing out step will be done within one or more separately controllableheaters indicated at 78 and 80, respectively, and thus the temperaturesin the heating zones 78A and 80A therewithin may be separately anddifferently regulated.

When a tapered portion 81 of desired length and shape has been produceda pair of shearing knives, or equivalent mean, 8`2 will operate to severthis tapered portion from the incoming bundle and then fingers 76 willmove outwardly to the position indicated at 78B and drag the taperedportion out of the heaters 78 and 80 and onto a supporting table 83 asindicated by dotted line 86 at a more rapid rate. Thereafter a secondpair of shears, or other known cutting means S4, will cut the taperedpor-tion 81 free from the gripped butt end 88. At this time the taperedportion 86 may be moved laterally of the table 83, as by a pusher 90,and onto a conveyor diagrammatically indicated at 92 for movementthrough an annealing oven or the like.

In FIG. 11 a plurality of tapered portions of multitibered ormultilament strands are shown collectively constituting an imagetransfer device 94 of the image enlarging type, and in this particulardevice one end 96 thereof has beeniinished to accommodate the face of acathode ray tube while the other end is arranged to fit against the rearsurface of a ground glass screen 98 or the like. This device 94, it willbe appreciated, is curved intermediate its ends. This curving can beaccomplished by either slowly heating each individual strand to asoftening temperature or heating groups of such strands or even theentire device to a softening temperature and allowing same to curve orsag into place. However, heating and curving of groups of strands ispreferred since on the one hand the heating `and softening periodrequired is not -as great `as when all strands are together and on theother hand would be much faster than individually curving each separatemultitibered or multilament strand.

In FIG. l2 is shown at 100 by way of example a different form of opticaldevice or component which the present invention may take, and it will beobvious that many other useful forms are also possible. This opticaldevice 100 is in fact a component which may be used between lenses of anoptical system to transfer an image from one curved face thereof to theother diiferently curved face thereof. Thus a change in field curvaturewithout a change in magnification can be effected. The componentnevertheless is formed by a very large number of very small strandscemented or fused together with each strand thereof in turn being formedof a plurality of individual light conducting elements or filaments ofhigh index transparent material optically insulated or opticallyisolated from all adjacent strands by means of a layer or coating ofclear transparent material of lower refractive index.

At places wherein the words image resolution have been used in variousparts of the foregoing specification with reference to optical devicesand optical components made in accordance with the present invention, itis intended that these words wil be interpreted in accordance with thephysical characteristics and requirements of the optical device orassociated means with which the improved image transfer device is to beused. For example, if the improved device is to form the face of atelevision tube which does not enlarge, it may look somewhat like thecomponent 100 shown in FIG. l2, although the cross-sectional size of theindividual filaments or light conducting elements thereof may be verymuch different from that required for a similarly appearing device beingused between lens elements of an optical system.

It is to be understood that when a low index glass is used as describedherein as the light-reflecting coating for the glass-forming the coresor centers of the rods or lillaments, that any two high and low indexglasses chosen to work together will be selected so that certain otherdesirable physical characteristics are also provided. For example,preferably, both glasses should be of good durability, should betransparent and colorless, and should have nearly the same coefficientof expansion (at least within the range from annealing to roomtemperatures). And, of course, both glasses should have nearly the samemelting characteristics or the low index glass forming the coatingshould have a slightly lower melting point.

Thus, it will be appreciated that a total reduction in size in theindividual fibers or iilaments of each fused together multiple elementstrand of the optical devices or components of the character describedof as much as 500 to l, or even more, can be produced, while stillhaving each individual element or lament thereof optically separatedfrom adjacent elements or filaments and thus each will retain itsselective light conducting properties and high light conductingeiciency.

Having described my invention, I claim:

1. The method of forming an optical image transfer component comprisingapplying to the side walls of each rod of a plurality of rigid elongatedtransparent glass rods of a relatively high refractive index, and ofsimilar size and cross-sectional shape, a relatively thin encirclingcoating of glass of a relatively low refractive index, positioning saidcoated rods in side-by-side parallel closely buuched contacting relationto each other so as toV form a compact bundle, evacuating the spacesurrounding said bundle and slowly raising the temperature of saidbundle so as to cause the contacting portions of adjacent coated rods tofuse together, increasing and controlling the temperature of the fusedbundled so that an end portion thereof will be maintained at a softenedtemperature, drawing from the softened end of said fused bundle aunitary strand of high and low index glasses having a cross-sectionalarrangement geometrically similar to that of said fused bundle but ofmaterially reduced size, severing said strand into a plurality ofseparate sections of substantially equal length, assembling a relativelylarge number of said sections together in side-by-side relation,repeating said fusing, heating, drawing, severing and assembling steps asuicient number of times to produce a very large number of individuallight-conducting elements each comprising a plurality of cores of highindex glass and relatively small predetermined size optically insulatedfrom one another by low index glass, fixedly securing said relativelylarge number of elements together, and optically finishing the oppositeends of said secured elements so as to provide an optical componenthaving entrance and exit areas of predetermined size and of likegeometric arrangement.

2. The method of forming an optical image transfer component comprisingapplying to the side walls of each rod of a plurality of rigid elongatedtransparent glass rods of relatively high refractive index, and ofsimilar size and cross-sectional shape, a relatively thin encirclingcoating of glass of relatively low refractive index, positioning saidcoated rods in side-by-side closely bunched contacting relation witheach other so as to form a compact bundle having substantially no spacetherein capable of including trapped air, slowly raising the temperatureof said bundle so as to cause the contacting portions of adjacent coatedrods to fuse together, increasing and controlling the temperature of thefused bundle so that an end portion thereof will be maintained at asoftening temperature, drawing from the softened end of said fusedbundle a unitary strand of high and low index glasses having across-sectional arrangement geometrically similar to that of said bundlebut of materially reduced size, severing said strand into a plurality ofseparate sections of substantially equal length, assembling a relativelylarge number of said sections together in side-by-side relation,repeating said fusing, heating, drawing, severing and assembling steps asufficient number of times to produce a very large number of individuallight-conducting elements each comprising a plurality of cores ofrelatively small predetermined size optically insulated from one anotherby low index glass, fixedly securing said elements together andoptically finishing the opposite ends of said secured elements so as toprovide an optical component having entrance and exit areas ofpredetermined size and of like geometric arrangement.

3. The method of forming an optical image transfer component comprisingapplying to the side walls of each rod of a plurality of rigid elongatedtransparent glass rods of relatively high refractive index, and ofsimilar size and cross-sectional shape, a relatively thin encirclingcoating of glass of a relatively low refractive index, positioning saidcoated rods in side-by-side parallel closely bunched contacting relationto each other so as to form a compact bundle having substantially nospace therein capable of including trapped air, evacuating the spacesurrounding said bundle and slowly raising the temperature of saidbundle so as to cause the contacting portions of adjacent coated rods tofuse together, increasing and controlling the temperature of the fusedbundle so that an end portion thereof will be maintained at a softeningtemperature, drawing from the softened end of said fused bundle aunitary strand of high and low index glasses having a cross-sectionalarrangement geometrically similar to that of said fused bundle but ofmaterially reduced size, severing said strand into a plurality ofseparate sections of substantially equal length, assembling a relativelylarge number of said sections together in side-by-side relation,repeating said fusing, heating, drawing, severing and as` sembling stepsa suicient number of times to produce a very large number of individuallight-conducting elements each comprising a plurality of cores ofrelatively small predetermined size optically insulated from one anotherby low index glass, fixedly securing said elements together andoptically finishing the opposite ends of said secured elements so as toprovide an optical component having entrance and exit areas ofpredetermined size and of like geometric arrangement.

4. The method of forming an optical image transfer component comprisingapplying to the side walls of each rod of a plurality of rigid elongatedtransparent glass rods of a relatively high refractive index, and of asimilar size and cross-sectional shape, a relatively thin cncirclingcoating of glass of a relatively low refractive index, positioning saidcoated rods in side-by-side parallel closely hunched contacting relationto each other so as to form a compact bundle having a plurality of smallspaces uniformly dispersed among the coated rods of said bundle, slowlyraising the temperature so as to cause the contacting portions ofadjacent coated rods to fuse together, increasing and controlling thetemperature of the fused bundle so that an end portion thereof will bemaintained at a softening temperature, drawing from the softened end ofsaid bundle a unitary strand of high and low index glasses having across-sectional arrangement geometrically similar to that of said bundlebut of materially reduced size, severing said strand into a plurality ofseparate sections of substantially equal length, assembling a relativelylarge number of said sections together in sideby-side relation,repeating said fusing, heating, drawing, severing and assembling steps asuliicient number of times to produce a very large number of individuallightconducting elements each comprising a plurality of cores ofrelatively small predetermined size optically insulated from one anotherby low index glass, tixedly securing said relatively large number ofelements together, and optically finishing the opposite ends of saidsecured elements so as to provide an optical component having er1-trance and exit areas of predetermined size and of like geometricarrangement.

5. The method of forming an optical image transfer component comprisingapplying to the side walls of each rod of a plurality of rigid elongatedtransparent rods of glass of relatively high refractive index and ofsimilar size and cross-sectional shape, a relatively thin encirclingcoating of glass of a relatively low refractive index, positioning saidcoated rods in side-by-side parallel closely hunched contacting relationto each other so as to form a compact bundle, slowly raising thetemperature of said bundle to cause the contacting portions of adjacentcoated rods to fuse together, increasing and controlling theternperature of the fused bundle so that an end portion thereof will bemaintained at a softened temperature, repeatedly drawing and severingfrom the softened end of said fused bundle multi-fibered tapered unitarystrands of high and low index glasses each having a cross-sectionalarrangement which is geometrically similar to that of said fused bundlebut of materially reduced size, assembling and securing a very largenumber of said tapered strands together in side-by-side hunched relationso as to form a component of appreciable size, and optically finishingthe opposite ends of the strands of said component so as to formentrance and exit areas of different sizes.

6. The method set forth in claim and additionally comprising the stepsof slowly raising the temperature of said component to a softeningtemperature and thereafter causing said component to assume apredetermined bent shape intermediate the entrance and exit areasthereof without materially changing the cross-sectional arrangement ofthe fibers thereof adjacent said entrance and exit areas.

7. The method of forming an optical image transfer component comprisingapplying to the side walls of a plurality of rigid elongated transparentglass rods of a relatively high refractive index, and of similar sizeand cross-sectional shape, a relatively thin encircling coating of glassof a relatively low refractive index, positioning said coated rods inside-by-side parallel closely hunched contacting relation to each otherso as to form a compact bundle, slowly raising the temperature of saidbundle to cause the contacting portions of adjacent coated rods to fusetogether, increasing and controlling the temperature of the fused bundleso that an end portion thereof will be maintained at a softenedtemperature, drawing from the softened end of the fused bundle a unitarymulti-fibered strand of high and low index glasses each having acrosssectional arrangement geometrically similar to that of said fusedbundle but of materially reduced size, severing said multi-hered strandinto separate members of substantially equal length, assembling saidmulti-fibered members into a side-by-side parallel closely hunchedcontacting relation to each other so as to form a compact bundle,heating an end portion of said bundle to fusing and softeningtemperature, and drawing from said lastmentioned end a unitaryrelatively thin multi-filament strand, severing said multi-filamentstrand into multi-filament threads of equal length, securing a verylarge number of said multi-filament threads together in side-by-siderelation so as to form a light-conducting component of appreciable size,and optically finishing at least one end of said component for thetransmission of light therethrough.

8. The method of forming a fiber optical light transfer devicecomprising applying to the side walls of each rod of a plurality ofrigid elongated transparent glass rods of a relatively high refractiveindex, and of substantially similar size and cross-sectional shape, arelatively thin encircling coating of glass of a relatively lowrefractive index, positioning said coated rods so as to have at least aselected region thereof in side-by-side parallel hunched contactingrelation to each other so as to form at said region a compact bundle,slowly raising the temperature of said bundle so as to cause thecontacting portions of adjacent coated rods to fuse together, increasingand controlling the temperature of the fused bundle so that an endportion thereof will he maintained at a softened temperature, drawingfrom the softened end a unitary strand of high and low index glasseshaving a cross-sectional arrangement geometrically similar to that ofsaid fused bundle but of materially reduced size, severing said strandinto a plurality of separate sections of substantially equal lengths,assembling a plurality of said sections together in side-by-siderelation, repeating said fusing, heating, drawing, severing andassembling steps a suicient number of times to produce a very largenumber of individual light-conducting elements each comprising aplurality of cores of high index glass and relatively smallpredetermined size optically insulated from one another by low indexglass, and iixedly securing said relatively large number of elementstogether so as to produce a light transfer device having entrance andexit areas of predetermined sizes.

9. The method of forming a ber optical light transfier device comprisingapplying to the side walls of each rod of a plurality of rigid elongatedtransparent glass rods of a relatively high refractive index, and ofsubstantially similar size and cross-sectional shape, a relatively thinencircling coating of glass of a relatively low refractive index,positioning said coated rods so as to have at least a selected regionthereof in side-by-side parallel hunched contacting relation to eachother so as to form at said region a compact bundle, evacuating thespace surrounding said compact bundle and slowly raising the temperatureof said compact bundle so as to cause the contacting portions ofadjacent coated rods to fuse together, increasing and controlling thetemperature of the fused bundle so that an end portion thereof will bemaintained at a softened temperature, drawing from the softened end aunitary strand of high and low index glasses having a cross-sectionalarrangement geometrically similar to that of said fused bundle but ofmaterially reduced size, severing said strand into a plurality ofseparate sections of substantially equal lengths, assembling a pluralityof said sections together in side-by-side relation, repeating saidfusing, evacuating, heating, drawing, severing and assembling steps asufficient number of times to produce a very large number of individuallight-conducting elements each comprising a plurality of cores of highindex glass and relatively small predetermined size optically insulatedfrom one another by low index glass, and xedly securing said relativelylarge number of elements together so as to produce a light transferdevice having entrance and exit areas of predetermined sizes.

l0. The method of forming a fiber optical light transfer devicecomprising applying to the side walls of each rod of a plurality ofrigid elongated transparent rods of glass of relatively high refractiveindex and of similar size and cross-sectional shape, a relatively thinencircling coating of glass of a relatively low refractive index,positioning said coated rods so as to have at least a selected regionthereof in side-by-side parallel hunched contacting relation to eachother so as to form at said region a cornpact bundle, slowly raising thetemperature of said bundle to cause the contacting portions of adjacentcoated rods to fuse together, increasing and controlling the temperatureof the fused bundle so that an end portion thereof will be maintained ata softened temperature, repeatedly drawing and severing from thesoftened end of said fused bundle multi-libered tapered unitary strandseach of high and low index glasses and having a cross-sectionalarrangement which is geometrically similar to that of the fused bundlebut of material reduced size, assembling and securing a very largenumber of said tapered strands together in side-hy-side hunched relationso as to form a light transfer device having entrance and exit areas ofpredetermined sizes.

1l. The method of forming a light transfer optical device which consistsof a closely packed group of generally parallel light-conducting hers ofhigh index glass separated from each other by layers of low index glass,said method comprising the steps of stacking in a parallel array aplurality of high index transparent glass rods each of which have beenpreviously coated with a thin layer of low index glass, holding saidarray of coated rods in contacting relation with each other, heatingsaid array so as to weld same into a firmly bonded bundle, heating atleast an end portion of said bundle and drawing same down into a strandthe size of which is only a fraction of the original size of said bundlewhile retaining suhs'tantially the original geometric cross-sectionalarrangement of said bundle, severing said strand into unit lengths,grouping and retaining said llengths in stacked relatively intimateside-by-side relation to each other, heating said group to weld saidlengths together, and repeating said drawing, severing and groupingsteps until an optical device of desired size is obtained.

12. The method of forming a bundle of light transfer bers of a givensmall cross-sectional size comprising coating a plurality of relativelylarge transparent high index rods of glass throughout the entire outerside surfaces thereof with relatively thin continuous coatings of lowindex glass, bundling said coated rods of glass with portions of saidcoated side surface portions thereof in adjacent relatively intimateside-by-side relation with each other, heating while holding saidadjacent portions of said coated rods of glass together to a temperaturesufficient to cause the adjacent coatings to fuse with each other andform a unitary bundle, and thereafter drawing the unitary bundle ofcoated rods down to said given fiber size while substantially retainingthe initial related cross-sectional geometrical arrangements of saidrods and coatings.

13. The method of forming a bundle of light transfer fibers of a givensmall cross-sectional size comprising coating a plurality of relativelylarge transparent high index rods of glass having relatively at sidesurface portions with relatively thin continuous coatings of low indexglass, bundling said rods together and causing said relatively datcoated side surface portions to be positioned in adjacent relativelyintimate side-by-side relation with each other, heating said bundlewhile retaining said relation to a temperature suicient to cause saidadjacent coatings to fuse with each other, and thereafter drawing saidunitary bundle of coated rods down to said given fiber size and in suchmanner as to cause portions of the side surfaces thereof to retain saidengagement and to substantially retain the initial cross-sectionalgeometrical relationship of said rods and coatings.

14. The method of forming a bundle of light transfer fibers of a givensmall cross-sectional size comprising coating a plurality of relativelylarge transparent high index hexagonal rods of glass throughout theentire outer side surfaces thereof with relatively thin continuouscoatings of low index glass, bundling said coated rods of glass withcoated side surface portions thereof in adjacent side-by-side relationwith each other, heating while pressing said adjacent portions of saidcoated rods of glass together to a temperature sufficient to cause theadjacent coatings to fuse with each other and thereafter drawing saidunitary bundle of coated rods down to said given fiber size and in suchmanner as to cause the major portions of the side surfaces thereof toassume substantially hexagonal side surface engagement with each other.

15. The method of forming an air-tight optical image transfer componentof appreciable exposed front and rear surface areas, said methodcomprising applying to the side walls of each rod of a plurality ofrigid elongated transparent glass rods of relatively high refractiveindex, a relatively thin encircling coating of glass of relatively lowrefractive index, positioning said coated rods with portions thereof inside-by-side closely bunched contacting relation with each other so asto form a compact bundle, slowly raising the temperature of said bundleso as to cause the contacting portions of the adjacent coated rods tofuse together, controlling the temperature of the fused bundle so thatan end portion thereof will be maintained at a softening temperature,drawing from the softened end of said fused bundle a unitary strand ofhigh and low index glasses having a cross-sectional arrangementgeometrically similar to that of said bundle but of materially reducedsize, severing said strand into a plurality of separate similarsections, assembling an appreciable number of said sections together inside-by-side closely hunched contacting relation, repeating saidassembling, heating, fusing, drawing, and severing steps so as toproduce the very large number of individual lightconducting elementsneeded for forming said optical component, and with each of saidelements comprising a plurality of high index glass cores of relativelysmall predetermined cross-sectional size optically insulated from oneanother by low index glass, assembling said individual light-conductingelements and heating said elements for such a time and at such atemperature as to cause said elements to fuse together and form saidair-tight component, and optically finishing the opposite faces of saidcomponent so as to provide thereon entrance and exit areas ofpredetermined sizes and with the opposite ends of said cores disposed inlike geometric arrangement.

References Cited in the tile of this patent UNITED STATES PATENTS1,751,584 Hansell Mar. 25, 1930 2,294,429 Stutz Sept. 1, 1942 2,313,296Lamesch Mar. 9, 1943 2,354,591 Goldsmith July 25, 1944 2,393,979 EverettFeb. 5, 1946 2,532,091 Everett Nov. 28, 1950 2,652,660 Kurz Sept. 22,1953 2,752,731 Altosaar July 3, 1956 2,825,260 OBren Mar. 4, 1958

